Diagnostic system for inflatable safety bag firing circuit

ABSTRACT

A circuit for firing the gas generating system of an inflatable safety bag device includes a capacitor which is charged from the battery at such time as the ignition switch is closed. A light emitter is connected to the capacitor so as to be energized during the charging of the capacitor. A sensor detects output from this light and controls the energization of a second light emitter. In the event the first light emitter emits light following the closure of the ignition switch, indicating proper operation of the circuitry, the second light emitter will be deenergized. Fiber optic bundles lead from both of the light emitters to a visual indicator assembly mounted on the dashboard of the vehicle. An alternate embodiment of the invention employs only a single light emitter diode which is normally energized and is deenergized in the event an inductive sensing means does not detect the proper operation of the charging circuitry.

United States Patent 1 Lewis et al.

[ July 10, 1973 DIAGNOSTIC SYSTEM FOR INFLATABLE SAFETY BAG FIRINGCIRCUIT Donald J. Lewis, Troy, Mich.; William Gordon, Knoxville, Tenn.;Robert W. Wulbrecht, Utica, Mich.

Allied Chemical Corporation, New York, N.Y.

Filed: Oct. 20, 1911 Appl. No.: 190,861

Inventors:

References Cited UNITED STATES PATENTS 1/1972 Dillman 340/52 H 4/1940Paul at al. 340/380 UX 6/1972 11/1971 9/1966 Pribonic 340/380 x PrimaryExaminer-Alvin H. Waring Attorney-Jonathan Plaut et al.

[57] ABSTRACT A circuit for firing the gas generating system of an inflatable safety bag device includes a capacitor which is charged fromthe battery at such time as the ignition switch is closed. A lightemitter is connected to the capacitor so as to be energized during thecharging of the capacitor. A sensor detects output from this light andcontrols the energization of a second light emitter. ln the event thefirst light emitter emits light following the closure of the ignitionswitch, indicating proper operation of the circuitry, the second lightemitter will be deenergized. Fiber optic bundles lead from both of thelight emitters to a visual indicator assembly mounted on the dashboardof the vehicle. An alternate embodiment of the invention employs only asingle light emitter diode which is normally energized and isdeenergized in the event an inductive sensing means does not detect theproper operation of the charging circuitry.

7 Claims, 3 Drawing Figures SERVICE \72 PATENTEU JUL 1 01973 3. 745 52 3SHEET 2 0F 2 l4 -A M I 28 1 62 10. "J 3 I 32 34 22 I 24 /'2 86 s2 s4 2g/ 46% $509 40 so fi'f 42 82 I F IG. 3

INVENTORS. :9 "T- DONALD J. LEWIS WILLtAM GORDON n ROBERT w. WULBRECHT92 BY: AIR BAG A V SERVICE X i Wk? ATTORNEY.

DIAGNOSTIC SYSTEM FOR INFLATABLE SAFETY BAG FIRING CIRCUIT BACKGROUND OFTHE INVENTION 1. Field of the Invention I This invention relates toapparatus for detecting the condition of readiness of a firing circuitfor a gas inflatable automotive safety device and signalling the driverof its findings.

2. Description of the Prior Art One of the most promising form of systemfor protecting the driver of an automotive vehicle against the hazardsof collisions involves bags which are inflated in a fraction of a secondupon the detection of the collision so as to extend between the driverand the vehicle to restrain the driver in his seat and cushion hisforward motion. The bags used with such systems are inflated by therelease of compressed gas stored in a container, by the generation ofgas by so-called pyrotechnic apparatus, or by some combination of thesetwo techniques.

One of the problems encountered in the design of such systems is theunusual burden placed on that portion of the equipment which initiatesthe release and/or generation of gas upon the-detection of a collisioncondition; hereinafter referred to as the firing circuit". This circuitmustoperate with an unusually high degree of reliability to initiate thegas generation and release process when the collision is detected. Inthe event of failure of the circuit to initiate firing upon theoccurrence of a collision the system will be useless and the operatorwill be subjected to the high forces associated with the impact. In theevent of false operation of the circuitry when no impact is detected thesudden inflation of the bags when not required is undesirable. Inaddition to these problems there is no way of testing the firing circuitafter it has been placed in association with the gas generatingapparatus in the vehicle. Additionally, the firing circuit may be calledupon to operate properly after having lain dormant in the vehicle for anumber of years during which the vehicle has been used without beinginvolved in a collision.

All of these problems have led to the invention of a diagnostic devicewhich checks the proper operation, and readiness for use of substantialsections of the firing circuitry during normal operation of the vehicle.As disclosed in United States Patent Application, Ser. No. 177,559,filed 9/2/71 entitled Diagnostic Firing Circuit, assigned to theassignee of the present invention, such circuitry preferably includes asignal lamp connected to the firing circuitry so as to be normallyenergized for a brief period of time during the normal operation of thevehicle, as when the ignition switch is closed. A sensor electricallyisolated from the energizing circuitry for the first lamp, so as not tobe subject to its failures, is adapted to monitor the proper operationof the first signal lamp and to control a second signal lamp so that thesecond lamp is energized at such time as the first lamp should normallyhave been energized but failed to light. In normal operation of thisdiagnostic system the first lamp will thus be lit for a few seconds uponclosure of the ignition switch and the second signal light will not beenergized. If that portion of the firing circuitry which is monitored bythe first signal lamp is defective in some way, the first signal lampwill fail to light and thereupon the second signal light will beenergized and stay lit until the ignition switch is opened. The signallights are disposed in the dashboard of the vehicle so as to be readilyvisible to the driver to warn of the improper condition of the firingcircuitry.

One of the problems associated with the implimentation of thisdiagnostic signal device arises from the need to monitor the operationof the first signal lamp in a manner independent of the first signallamp circuitry, so that failureof that circuitry will not adverselyaffect the operation of the second signal lamp. This monitoring may bereadily accomplished by a photo-detector positioned so as to besensitive to the light emission of the first signal device, or by someother sensor positioned to detect the energy, electrical, thermal, andmagnetic generation associated with the proper operation of the firstsignal device. However, if the first signal device is positioned on thedashboard of the vehicle so as to be visible to the driver, a mechanismmust be provided to isolate thesensor from stray optical or thermalemissions not associated with the first signal. Most important, however,is the possibility of the induction of electro-magnetic energy into thelamp circuit thence into the firing circuit.

SUMMARY OF THE INVENTION In order to obviate this difficulty, thepresent invention contemplates a system wherein the first lamp is notsupported in the vicinity of the vehicle dashboard but is ratherpositioned with the balance of the firing circuit at a location normallyhidden to the vehicle driver. At this location the sensor can easily beisolated from stray optical, thermal, and electrical, etc. signals sothat it is solely sensitive to the proper operation of the first signaldevice. The optical signals from the lamps are then conveyed to thedriver through a fiber optics bundle which extends between the signallamps and a visual signal device supported in the vicinity of thevehicle dashboard. The fiber optics light conductor can only fail if itis physically broken which will probably only occur during a collisionsituation. Removing the lamp from the dashboard area to a normallyinaccessible area increases its life expectancy by virtue of removing itfrom those forces which come to play in the area of the dashboard.

In the first'embodiment of this system, both the first and second signallamps are disposed at a location remote from the dashboard and theirlight emission is conveyed to the dashboard througlh fiber opticbundles. In a second embodiment of the invention, the first signal lightis eliminated and the proper condition of the firing circuit is detectedby inductively sampling the current flow through the firing circuitafter the closure of the ignition. This inductive detector controls theoperation of a single signal lamp which is normally lit only during thecharging cycle so as to reenergize that lamp in the event of an impropercurrent flow during the testing. Failure of the signal lamp to lightduring the starting cycle will warn the operator of some defect, eitherin the firing or the diagnostic circuitry. This defect may be only thefailure of the light emitting device itself, but informs the driver ofthe need for checking the circuitry.

Other objectives, advantages, and applications of the present inventionwill be made apparent by the following detailed description of twopreferred embodiments of the invention. The description makes referenceto the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a firing system diagnostic circuitformed in accordance with a first preferred embodiment to the invention;

FIG. 2 is a perspective view of the dashboard area of a vehicle, withsections broken away, illustrating the physical position of thecomponents illustrated schematically in FIG. 1; and

FIG. 3 is a partial schematic diagram of a firing system diagnosticcircuit constituting a modification of the circuit of FIG. 1.

The sensor is schematically illusated as having a roller which rides onthe outer side of a curved band 22. The band connects to the inputterminal of the switch and the roller, which is conductive, ridesbetween a normally closed terminal 24 and a normally open terminal 26.In the event of an impact of the type intended to inflate the bags, theroller 20 moves away from the contact 24 and into abutment with thecontact 26 thereby disconnecting the contact 24 from the input terminaland connecting contact 26 to the input.

The battery 14 has its negative terminal connected to ground and itspositive terminal connected to an ignition switch 28. The other terminalof the ignition switch is connected to a low pressure sensor switch 30.The sensor switch 30 is of the type that is desclosed in United StatesPatent Application Ser. No. 139,492,

filed May 3, 1971, entitled Low Pressure Indicator for Air Bag SafetySystem". The switch is closed as long as the pressure in the associatedgas tank issufficiently high to inflate the bag in the event of acollision. If the pressure falls below this threshhold level, the switch30 o ens.

The input terminal 22 of the impact sensor switch 11 is connected to thebattery, when the switches 28 and 30 are closed, through a set of diodes32, 34, 36 and 38. The diodes 32 and 34 are connected in parallel to oneanother as are the diodes 36 and 38 and the two pairs are connected inseries. Each of the diodes has the voltage rating and current capacitysufficient to carry the entire firing current and in a normal,non-redundant circuit, only a single diode would be provided to performthe function of these four elements.

This redundant arrangement insures proper operation of the systemdespite the failure of any one of the diodes. If any of the diodesbecomes open circuited, its

companion diode in the parallel set is operative to carry the current.If any of the diodes'become short circuited, the other parallel pairprovides unidirectional current limiting capability.

Thus, in normal operation of the circuit, with the ignition switchclosed and the low pressure sensor switch 30 closed, if the vehicle wereto become involved in a collision which would cause the ball 20 of thesensor switch 11 to move into contact with the terminal 26 of the fullcurrent of the battery would pass through the electro-explosive devices12, which have one end grounded, through the diodes 32, 34, 36, 38 andthe impact sensor 10.

A capacitor 40 is provided in the circuit to act as an alternate powersource for the electro-explosive de vices 12 in the event of failure ofthe battery 14 at the time of impact. The capacitor is large, having arate of 12,000 microfarands in the preferred embodiment of theinvention. One end of the capacitor 40 is connected to ground through aconductor 42. The other end of the capacitor connects to the positiveterminal of the battery through a light emitter 44 which is connected tothe noramlly closed contact 24 of the impact sensor switch 10. Thus, thecapacitor 40 is charged to substantially the potential of the battery 14when the ignition switch 28 and the low pressure sensor switch 30 areclosed and the impact sensor switch 11 is in its normal condition.

A resistor 46 provides an alternate charging path for the capacitor 40through a conductor 48 in the event that the light emitter 44 is burnedout or is removed from its socket. The resistor 46 has a substantiallyhigher resistance than the lamp so that when the lamp is in place thecharging of the capacitor occurssubstantially through the lamp. In thepreferred embodiment the lamp may have a resistance of ohms and theresistor 46 may have a value of 27,000 ohms.

When the capacitor 40 is disconnected from the battery it is dischargedat a relatively low rate through the resistor 46 and a group of fourparallel resistors 50a, 50b, 50c and 50d. These resistors 50 are inseries with the resistor 46 across the capacitor. The four resistorshave a relatively low resistance such as approximately 180 ohms each.Four are provided so that in the event of one of the resistors becomingopen the path resistance will not be increased appreciably.

The capacitor 40 thus forms an alternate power source for activating theelectro-explosive devices 12 at such time as the sensor switch 10activates the circuit. In the event of an impact which disconnects thebattery, as sometimes occurs because of'the high inertia of the battery,the capacitor 40 will quickly discharge through the electro-explosivedevices which have a resistance of about 4.50 ohms each. This discharge.path includes a pair of diodes 52 and 54 which are disposed in parallelwith one another to provide a firing path even if one of the unitsopens.

Because of the discharge of the capacitor 40 through the resistors 46and 50 after the ignition switch 28 is opened, when the driver laterrestarts the vehicle the capacitor 40 will initially be in a dischargedstate. As soon as the ignition switch 28 is closed the capacitor beginsto charge through the diodes 32, 34, 36 and 38, the sensor switch 10 andthe light emitting diode 44. The potential difference which existsbetween the capacitor 40 and the battery during this charging periodcauses the light emitter 44 to light. The constants of the circuit aresuch that the charging normally takes about 5 seconds. After that timethe capacitor will have substantially the same charge as the battery,and no current will flow through the light emitter 44.

The light emitter 44 is disposed, along with the balance of the firingcircuit, at a position on the vehicle which is not immediatelyaccessible and not observable to the driver of the vehicle. Accordingly,the driver cannot view the light. A light activated switch 56 isdisposed with the balance of the firing circuitry in the driver-remotelocation and is physically positioned with respect to the light emitter44 so as to receive light at such time as the lamp is energized. Thelight sensitive switch is a device which is normally nonconductive andbecomes conductive when a proper direct current potential exists betweenits anode and cathode and it receives light.

In the preferred embodiment of the invention, the light sensitive switch56 constitutes a switch having one end grounded and the otherendconnected to the ignition switch through current limiting resistor 58.Before the ignition switch 28 is closed the unit 56 is in itsnonconductive condition. As the ignition switch is closed if the lightemitter 44 lights, the unit 56 will go into its conductive state withina few milliseconds and will remain in that state until the ignitionswitch opens, despite the subsequent turnoff of the light emitter 44.

The switch 56 shunts a second light emitter 60 which is also disposedwith the circuitry at the position remote and not observable to thedriver. When the unit 56 is in its conductive state it shorts out thelight emitter 60 so that the lamp is not energized. In the normaloperation of the circuit when the ignition switch 28 is closed, thelight emitter 60 will only be energized for the few millisecondsrequired for the light emitter 44 to reach a sufficient illuminationlevel to energize the unit 56 into its conductive state wherein itshorts out the light emitter 60. Thus, in normal operation of thevehicle the light emitter 60 will not be lit when the ignition switch ison. However, in the event of failure of the light emitter 44 to lightupon closure of the ignition switch, for any number of reasons, the lamp60 will remain burning as long as the ignition switch is closed.

The circuit is completed by a spark gap 62 which is disposed between theignition switch and ground and acts as a voltage limiter for the entiresystem. In the event that a high voltage signal is somehow impressedbetween the battery and ground the gap 62 will limit the voltageprovided to the firing circuit.

It will be noted that the schematic diagram is somewhat unusual in theinterconnection of the elements. For example, the right-hand end of thecapacitor 40 is illustrated in FIG. 1 as connected to ground through theconnector 42 which also joins one end of the electro-exp'losive devices12 and one end of the resistors 50a, 50b, 50c, and 50d to ground. Thisconnection 42 represents the actual manner in which the circuit is wereeach independently grounded, the lamp wouldnot operate to test all theirgrounds.

As has been previously noted, either an open or a short in the diodes32, 34, 36 and 38 will be corrected by their redundancy. In a similarmanner the only malfunction of the diodes 52 and 54 which could affectthe system would be a short in one of the diodes and in that event thecapacitor 40 would effectively be shorted and the light emitter 44 wouldnot be lit by closure of the ignition switch. A short in the resistor 46would produce the same effect. If the resistor 46 became opened thesystem would still operate properly as long as the light emitter 44 wasnot opened. It should be noJed that when the light emitter 44 is open,charging of the capacitor takes place through the resistor 46, and thelight emitter 60 will remain lit but the system will still be incondition to inflate the bags in the event of an impact. If thecapacitor 40 becomes open the light emitter 44 will not light upon theignition switch closing and if the capacitor 44 becomes shorted thelight emitter 44 will remain lit as long as the ignition switch isclosed.

Since the light emitter 44 will not light if the low pressure switch 30is open the system also provides a check for low pressure and eliminatesthe need for a separate low pressure indicator lamp which was previouslyconsidered as required for such systems.

All of the components thus far described are positioned in a singleelectronic assembly, generally indicated at in FIG. 2, which is disposedat some convenient location in the vehicle not readily observable by thedriver such as in an area behind the dashboard. Thus, the light emitters44 and 60 are not normally visible to the driver. The driver is providedwith information relative to the condition of the safety system by asignal 72 which is conveniently positioned on the dashboard of thevehicle, preferably in the region of the other vehicle instruments, soas to be readily observable by the driver. The indicator 72 simplyconsists of a translucent panel.

The light emitter 44 is connected to the rear of the indicator 72through a light conductor 76, which preferably takes the form of abundle of optically conductive fibers. Such fibers are well known in theart and are operative to provide illumination behind the indicator 72 atsuch time as the light emitter 44 is energized. Similarly, the lightemitter 60 is connected to the rear of the indicator 72 through asimilar bundle of optical fibers 78 so as to illuminate the sign at suchtime as the light emitter 60 is illuminated.

The driver may determine the condition of the light emitters 44 and 60by observing the signal 72. In the normal operation of the vehicle thesignal 72 will be lit for a few seconds required to charge the capacitor40 after the ignition switch is closed indicating proper operation ofthe circuitry. In the event that the light emitter 44 fails to lightafter the ignition switch is closed, the light emitter 60 will remainon, providing a signal to the driver through the signal 44.

By reason of the positioning of the light emitters 44 and 60 in theremote location 70 where they are shielded from extraneous influenceswithout any difficulty being encountered in physically positioning thelight activated switch 56 with respect to the light emitter 44 so thatit is only sensitive to radiation from the lamp. 7

FIG. 3 illustrates an alternate embodiment of the invention wherein onlya single signal lamp is employed. Much of the electrical circuitry,employed in this embodiment is identical to that employed in thecircuitry of FIG. 1, and the same numerals are used for the element ofboth circuits. The system of FIG. 3 differs from the system of FIG. 1 inthat the light emitter 44 of FIG. 1 is replaced by an iron core pulsetransformer 80. The secondary of the transformer 80 has one end groundedand the other end coupled to the gate of a silicon controlled rectifier82.

The anode-cathode circuit of the rectifier is disposed in series with alamp 84 and a current limiting resistor 86 between the ignition switch28 of the vehicle and ground. When the controlled rectifier isnonconductive the lamp is then energized by the current passing from thepositive terminal of the battery to ground, when the controlledrectifier is in its conductive state the lamp 84 is not energized.

In the normal operation of the circuitry when the ignition switch isclosed the initial current surge to the capacitor 40 causes a pulse tobe induced in the secondary of the transformer 80. This pulse is appliedto the gate of the controlled rectifier 82 and causes the rectifier tobe conductive. Thereafter, until the ignition siwtch 28 is again opened,the lamp 84 will remain out. In the event of some improper operation ofthe diagnostic circuitry, which prevents the charging of the capacitor40 upon closing of the ignition switch, no pulse will be provided to thegate of the controlled rectifier 82 and the controlled rectifier willremain in its nonconductive state, and the lamp 84 will be lit.

The circuitry thus far disclosed is positioned in an area inaccessibleto the driver of the vehicle, in the same manner as the circuitry 70 ofFIG. 2. The driver is made aware of the condition of lamp 84 by a fiberoptics bundle 90 extending between the lamp 84 and a signal device 92disposed on the dashboard of the vehicle in a prominent location. Theoperator will be informed of some defect in the diagnostic circuitry bythe causing of the signal 92 to light.

By means of this single lamp circuit the driver will readily be advisedof the condition of the circuitry.

Having thus described our invention, we claim:

1. Diagnostic circuitry, adapted for use in a gas inflatable safetybag'system of a motor vehicle for signalling to the driver of thevehicle the condition of a firing circuit having a capacitor adapted tobe charged from the vehicles battery upon closure of the vehiclesignition switch, comprising a light emitting device connected to saidfiring circuit and operable to be energized at such time as saidcapacitor is being charged from said battery; visual signal meansdisposed adjacent to the vehicle driver position and remote from saidlight emitting device; and light conductive means coupling said lightemitting device to said visual signal means.

2. The diagnostic circuitry of claim 1 including a sensorphysicallydisposed adjacent tosaid light emitting device and being operative tosense its state of opertion and a second light emitting device operativeto be energized by the sensor in the event of failure of the aforesaidlight emitting device to be energized.

3. In a vehicle having an inflatable safety system including a firingcircuit for initiating the inflation of said system having a capacitoradapted to be charged from the vehicles battery upon closure of thevehicles ignition switch, diagnostic circuitry comprising a lightemitting device operative to be energized during such time as saidcapacitor is being charged from said battery; a visual signal devicedisposed in said vehicle at a location remote from said light emittingdevice so as to be visible to the driver of the vehicle; and lightconductive means extending between said light emitting device and saidsignal device operative to change the state of said signal device atsuch time as the light emitting device changes state.

4. The firing circuit of claim 3 including a sensor means disposedadjacent to and responsive to energization of said light emittingdevice, and a second light emitting device associated with said sensormeans, said sensor means being operable to prevent energization of saidsecond light emitting device upon energization of the aforesaid lightemitting device.

5. Diagnostic means, adapted for use in a gas inflatable safety bagsystem of a motor vehicle for signalling to the driver of the vehiclethe condition of firing circuitry having a capacitor adapted to becharged from the vehicles battery upon closure of the vehicles ignitionswitch, comprising a first light emitting device operative to beenergized at such time as said capacitor is being charged from saidbattery; a sensor physically disposed adjacent to said first lightemitting device and being operative to sense its state of operation; asecond light emitting device operatively connected to said sensor sothat the second light emitting device is operable to be energized in theevent of failure of the first light emitting device to be energized;visual signal means disposed adjacent to the driver position and remotefrom said first light emitting device; and light conductive meanscoupling each of said light emitting devices to said visual signalmeans.

6. The diagnostic means of claim 5 wherein said light conductive meansconstitute a bundle of optically conductive fibers.

7. In a vehicle having an inflatable safety system including a firingcircuit for initiating inflation of said system and a vehicle battery,an electric power storage device connected to the vehicle battery duringthe normal operation of the circuitry and disconnected therefrom atother times; means for discharging said power storage device; means forsensing the potential difference between said battery and said powerstorage device including a light emitting device; a signal devicedisposed adjacent to the vehicle driver position and remote from saidfirst light emitting device; and light conductive means coupling saidlight emitting device and said visual signal means.

1. Diagnostic circuitry, adapted for use in a gas inflatable safety bagsystem of a motor vehicle for signalling to the driver of the vehiclethe condition of a firing circuit havinG a capacitor adapted to becharged from the vehicle''s battery upon closure of the vehicle''signition switch, comprising a light emitting device connected to saidfiring circuit and operable to be energized at such time as saidcapacitor is being charged from said battery; visual signal meansdisposed adjacent to the vehicle driver position and remote from saidlight emitting device; and light conductive means coupling said lightemitting device to said visual signal means.
 2. The diagnostic circuitryof claim 1 including a sensor physically disposed adjacent to said lightemitting device and being operative to sense its state of operation anda second light emitting device operative to be energized by the sensorin the event of failure of the aforesaid light emitting device to beenergized.
 3. In a vehicle having an inflatable safety system includinga firing circuit for initiating the inflation of said system having acapacitor adapted to be charged from the vehicle''s battery upon closureof the vehicle''s ignition switch, diagnostic circuitry comprising alight emitting device operative to be energized during such time as saidcapacitor is being charged from said battery; a visual signal devicedisposed in said vehicle at a location remote from said light emittingdevice so as to be visible to the driver of the vehicle; and lightconductive means extending between said light emitting device and saidsignal device operative to change the state of said signal device atsuch time as the light emitting device changes state.
 4. The firingcircuit of claim 3 including a sensor means disposed adjacent to andresponsive to energization of said light emitting device, and a secondlight emitting device associated with said sensor means, said sensormeans being operable to prevent energization of said second lightemitting device upon energization of the aforesaid light emittingdevice.
 5. Diagnostic means, adapted for use in a gas inflatable safetybag system of a motor vehicle for signalling to the driver of thevehicle the condition of firing circuitry having a capacitor adapted tobe charged from the vehicle''s battery upon closure of the vehicle''signition switch, comprising a first light emitting device operative tobe energized at such time as said capacitor is being charged from saidbattery; a sensor physically disposed adjacent to said first lightemitting device and being operative to sense its state of operation; asecond light emitting device operatively connected to said sensor sothat the second light emitting device is operable to be energized in theevent of failure of the first light emitting device to be energized;visual signal means disposed adjacent to the driver position and remotefrom said first light emitting device; and light conductive meanscoupling each of said light emitting devices to said visual signalmeans.
 6. The diagnostic means of claim 5 wherein said light conductivemeans constitute a bundle of optically conductive fibers.
 7. In avehicle having an inflatable safety system including a firing circuitfor initiating inflation of said system and a vehicle battery, anelectric power storage device connected to the vehicle battery duringthe normal operation of the circuitry and disconnected therefrom atother times; means for discharging said power storage device; means forsensing the potential difference between said battery and said powerstorage device including a light emitting device; a signal devicedisposed adjacent to the vehicle driver position and remote from saidfirst light emitting device; and light conductive means coupling saidlight emitting device and said visual signal means.